In a semiconductor fabrication facility, the exhaust of various gases generated from the facility is an important aspect of the total fabrication process. Not only from a personnel health and safety point of view that the exhaust must be treated for converting various toxic components of the gases into non-toxic components, but also from the process reliability point of view of maintaining a constant exhaust pressure in exhaust duct works such that the chamber pressure of a process machine which has its exhaust connected to the exhaust duct works does not fluctuate with the pressure fluctuations in the duct works.
Various exhaust gases are produced in a semiconductor fabrication facility, these include general exhaust, scrubbed exhaust and solvent exhaust. For exhausting the general exhaust and the solvent exhaust, a system typically includes duct works, exhaust fans, by-passes, and stacks. For handling the scrubbed exhaust, a scrubber must be used for treating the exhaust before they can be released to the atmosphere. A by-pass system is normally provided which allows the drawing of outside air when the pressure at the suction side of the blower exceeds a preset value. In a general exhaust system, heat dissipated by the process equipment is normally removed. The general exhaust therefore does not normally contain acids, caustics, or solvents. In a solvent exhaust system, air containing solvents from the process equipment is removed. The equipment used in the exhaust system therefore requires to be explosion-proof for safety reasons. In the scrubbed exhaust system, air containing acids, caustics from the process equipment is removed. Various caustics exhaust gases such as ammonia, silane, or other toxic gases connected to a scrubber system for treatment. A wet scrubber can be used to remove acids and caustics from an exhaust air by washing the air with a solvent such as water. The waste water from the scrubber is then sent to a neutralization plant in a waste treatment area of the fabrication facility. A dry scrubber can also be used to remove toxic substances from an exhaust air by absorbing the substances into a scrubber material, typically at an elevated temperature. The scrubber material can be replaced when it is saturated with the toxic substances.
The various exhaust systems must be connected to a process machine via duct works. For instance, when exhausting from an atmospheric pressure chemical vapor deposition (APCVD) chamber or from a low pressure chemical vapor deposition (LPCVD) chamber, spent reactant gases and reaction by-products are normally exhausted to a scrubbed exhaust system for treatment before it is released to the atmosphere. An effective exhaust system for taking away such spent reactant gases and reaction by-products is therefore an important step of the chemical vapor deposition process. The spent reactant gases must be carried away such that the efficiency of the deposition process is not affected. Furthermore, the reaction by-products such as particles must also be carried away and prevented from depositing on the wafer surface as contaminants.
In an atmospheric pressure chemical vapor deposition chamber, the pressure of the chamber is kept only slightly below the atmospheric pressure, i.e., at approximately -0.5 inch H.sub.2 O pressure. The exhaust from an APCVD chamber is normally directly connected to factory exhaust duct works in order to take away the spent reactant gases and reaction by-products. However, the pressure in factory exhaust duct works is not stable since the duck works are connected to a multiple number of process machines. In a chemical vapor deposition process, the maintenance of a constant chamber pressure is important for achieving the depositions of high quality films. When the pressure in the chamber is not constant, the deposition process fluctuates and films of poor quality and uniformity are thus produced. One attempt to improve the chamber pressure consistency in a chemical vapor deposition chamber is the use of an exhaust blower to compensate for the pressure fluctuations in the factory exhaust duct works and to assist in pressure control. This is shown in FIG. 1.
FIG. 1 shows a conventional exhaust system for an atmospheric pressure chemical vapor deposition chamber 12. An exhaust conduit 14 removes the exhaust gas from chamber 12 through a butterfly valve, or throttle valve 16. The throttle valve 16 is normally only partially opened to allow an exhaust gas to pass into conduits 18 and 20 into the factory exhaust duct works. An exhaust blower 24 is added to the system which is powered by an AC power supply 26 and controlled by switch 36 for transporting the exhaust gas taking exhaust from conduits 28 into conduit 32 and 20. The use of the exhaust blower 24 helps the stabilization of pressure in conduit 20 that is connected to the factory exhaust duct works 34. However, since the exhaust blower 24 is a single-speed blower, in order to maintain a suitable pressure in the APCVD chamber 12, the throttle valve 16 has to be substantially closed.
When the throttle valve 16 is in a substantially closed (or only slightly opened) position several problems can occur. First, due to the small opening of the throttle valve 16, a minute fluctuation in the exhaust pressure in conduit 20 can lead to in a large pressure fluctuation in the deposition chamber 12. The pressure fluctuation in the exhaust conduit 20 is therefore greatly amplified as large pressure fluctuations in the deposition chamber 12. Secondly, at a substantially closed position, the throttle valve 16 is more proned to gather particulate deposits on its surface. The particulate deposits in a powdery form become a source of serious contamination for the chamber 12. During any pressure fluctuations in the chamber 12, a back-fill of the contaminating particles from the throttle valve 16 becomes possible. Such back-fill causes contamination either to the chamber wall inside the deposition chamber 12 or to the wafer surface. The conventional exhaust system, even when assisted by an exhaust blower, does not function properly for maintaining a constant pressure in an APCVD or LPCVD chamber.
It is therefore an object of the present invention to provide an apparatus for regulating chamber pressure in a process chamber that does not have the drawbacks or shortcomings of the conventional exhaust systems for such process chambers.
It is another object of the present invention to provide an apparatus for regulating chamber pressure in a process chamber that allows the use of an exhaust blower for assisting the exhaust of reaction by-products from the deposition chamber.
It is a further object of the present invention to provide an apparatus for regulating chamber pressure in a process chamber that utilizes an exhaust blower and an inverter for regulating the blower speed such that the chamber pressure can be suitably adjusted by regulating the blower speed.
It is another further object of the present invention to provide an apparatus for regulating chamber pressure in a process chamber by utilizing a pressure regulating system consisting of a pressure gauge, a pressure controller, and an inverter for regulating the speed of the exhaust blower such that a consistent exhaust pressure can be maintained in the factory exhaust duct works.
It is still another object of the present invention to provide an apparatus for regulating chamber pressure in a process chamber by utilizing an automated feedback system of measuring the pressure in factory exhaust duct works and then regulating a blower speed for exhausting a suitable amount of gas from a deposition chamber such that the pressure in the factory exhaust duct works can be maintained substantially constant.
It is yet another object of the present invention to provide a chemical vapor deposition system that includes a deposition chamber and a pressure regulating system which utilizes a pressure gauge and an inverter for regulating the speed of an exhaust blower such that the exhaust pressure in factory exhaust duct works can be maintained consistent.
It is still another further object of the present invention to provide an exhaust regulating system by utilizing an inverter capable of regulating an AC power frequency at between about 20 and about 60 kHz for controlling the speed of an exhaust blower.
It is yet another further object of the present invention to provide a method for controlling chamber pressure in a process chamber by sensing a pressure in a factory exhaust conduit and comparing the pressure to a desirable exhaust pressure and then regulating the speed of an exhaust blower to thus achieve the desirable exhaust pressure.